Adjustable achromatic collimator assembly for endpoint detection systems

ABSTRACT

Implementations disclosed describe a collimator assembly having a collimator housing that includes an interface configured to optically couple to a process chamber that has a target surface, and a port to receive an optical fiber to deliver, to an enclosure formed by the collimator housing, a first (second) plurality of spectral components of light belonging to a first (second) range of wavelengths, and an achromatic lens located, at least partially, within the enclosure formed by the collimator housing, the achromatic lens to direct the first (second) plurality of spectral components of light onto the target surface to illuminate a first (second) region on the target surface, wherein the second region is substantially the same as the first region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending U.S. Pat.Application No. 16/947,639 filed Aug. 11, 2020, which is incorporatedherein by reference.

TECHNICAL FIELD

This instant specification generally relates to fabrication ofintegrated circuits and other semiconductor devices in process chambers.More specifically, the instant specification relates to adjustableend-point detection systems for precise product control in devicemanufacturing.

BACKGROUND

Manufacturing of microelectronics and integrated circuit devices ofteninvolves performing numerous operations on semiconductor, dielectric andconductive substrates. Examples of these operations include oxidation,diffusion, ion implantation, thin film deposition, cleaning, etching,lithography, and so on. Materials manufactured in this manner mayinclude monocrystals, semiconductor films, fine coatings, and numerousother substances used in electronic device manufacturing and otherpractical applications. As atoms of selected types are added (e.g., viadeposition) to substrates or removed (e.g., via etching) from thesubstrates, efficient and precise endpoint monitoring techniques (andsystems) become valuable. Under-etching, as well as over-etching (andsimilarly, under-deposition and over-deposition), may result insubstandard and even malfunctioning devices. Optical control systems,which allow real-time monitoring of various stages of devicemanufacturing, significantly improve quality of the products. This isespecially useful given that the demands to the quality of semiconductordevices are constantly increasing.

SUMMARY

In one implementation, disclosed is a collimator assembly that includesa collimator housing and an achromatic lens. The collimator housingincludes an interface configured to optically couple to a processchamber that has a target surface and a port to receive an opticalfiber. The optical fiber is to deliver, to an enclosure formed by thecollimator housing, a first plurality of spectral components of lightthat belong to a first range of wavelengths and a second plurality ofspectral components of light belonging to a second range of wavelengths.The first range is within a 400-700 nm interval of wavelengths, and thesecond range is outside the 400-700 nm interval of wavelength. Theachromatic lens is located, at least partially, within the enclosureformed by the collimator housing. The achromatic lens is to direct thefirst plurality of spectral components of light onto the target surfaceto illuminate a first region on the target surface. The achromatic lensis further to direct the second plurality of spectral components oflight onto the target surface to illuminate a second region on thetarget surface so that the second region is substantially the same asthe first region.

In another implementation, disclosed is an endpoint detection systemthat includes a source of light, a collimator housing, an achromaticlens, a light detector, and a processing device. The source of light isto output a first plurality of spectral components of light belonging toa first range of wavelengths and a second plurality of spectralcomponents of light belonging to a second range of wavelengths. Thefirst range is within a 400-700 nm interval of wavelengths, and thesecond range is outside the 400-700 nm interval of wavelength. Thecollimator housing includes an interface configured to optically coupleto a process chamber that has a target surface. The collimator housingalso includes a port to receive an optical fiber to deliver, to anenclosure formed by the collimator housing, the first plurality ofspectral components of light belonging to a first range of wavelengthsand the second plurality of spectral components of light belonging to asecond range of wavelengths. The achromatic lens is located, at leastpartially, within the enclosure formed by the collimator housing. Theachromatic lens is to direct the first plurality of spectral componentsof light onto the target surface to illuminate a first region on thetarget surface, and direct the second plurality of spectral componentsof light onto the target surface to illuminate a second region on thetarget surface, so that the second region is substantially the same asthe first region. A second optical fiber is to collect a first pluralityof reflected, from the target surface, spectral components of lightproduced by the first plurality of spectral components of light directedonto the target surface. The second optical fiber is further to collecta second plurality of reflected, from the target surface, spectralcomponents of light produced by the second plurality of spectralcomponents of light directed onto the target surface. The light detectorto receive, via the second optical fiber, the first plurality ofreflected spectral components of light and the second plurality ofreflected spectral components of light. The processing device,communicatively coupled to the light detector, is to determinereflectance of the target surface, based on the received first pluralityof reflected spectral components of light and the received secondplurality of reflected spectral components of light.

In another implementation, disclosed is a method to output, by a sourceof light, a first plurality of spectral components of light belonging toa first range of wavelengths and a second plurality of spectralcomponents of light belonging to a second range of wavelengths. Thefirst range is within a 400-700 nm interval of wavelengths, and thesecond range is outside the 400-700 nm interval of wavelength. Themethod disclosed is further to direct, through an achromatic lens, thefirst plurality of spectral components of light onto a target surface tocause a first region on the target surface to be illuminated. The methoddisclosed is further to direct, through the achromatic lens, the secondplurality of spectral components of light onto the target surface tocause a second region on the target surface to be illuminated, so thatthe second region is substantially the same as the first region. Themethod disclosed is further to collect, by a second optical fiber, afirst plurality of reflected, from the target surface, spectralcomponents of light produced by the first plurality of spectralcomponents of light directed onto the target surface. The methoddisclosed is further to collect, by the second optical fiber, a secondplurality of reflected, from the target surface, spectral components oflight produced by the second plurality of spectral components of lightdirected onto the target surface. The method disclosed is further toreceive, by a light detector, via the second optical fiber, the firstplurality of reflected spectral components of light and the secondplurality of reflected spectral components of light. The methoddisclosed is further to determine, by a processing devicecommunicatively coupled to the light detector, a reflectance of thetarget surface, based on the received first plurality of reflectedspectral components of light and the received second plurality ofreflected spectral components of light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically a manufacturing machine that includes aspatially adjustable broadband collimator assembly, for precise opticalcharacterization of targets within a process chamber, in accordance withsome implementations of the present disclosure.

FIG. 2 illustrates schematically an exemplary achromatic (broadband)collimator assembly, for precise optical characterization of targetswithin a process chamber, in accordance with some implementations of thepresent disclosure.

FIGS. 3A-D illustrate schematically advantages of using achromatic(broadband) collimators for precise optical characterization of targetswithin a process chamber, in comparison with a conventional collimator,in accordance with some implementations of the present disclosure.

FIG. 4 illustrates schematically an exemplary collimator assembly havingadjustable alignment, for precise optical characterization of targetswithin a process chamber, in accordance with some implementations of thepresent disclosure.

FIG. 5 illustrates schematically a tilted exemplary collimator assemblyhaving adjustable alignment, for precise optical characterization oftargets within a process chamber, in accordance with someimplementations of the present disclosure.

FIG. 6 illustrates schematically a side view of an exemplary collimatorassembly having adjustable alignment, in accordance with someimplementations of the present disclosure.

FIG. 7 is a flow diagram of one possible implementation of a method ofdeploying a broadband collimator assembly for precise opticalcharacterization of targets within a process chamber, in accordance withsome implementations of the present disclosure.

FIG. 8 is a flow diagram of one possible implementation of a method ofadjusting tilt of an adjustable collimator assembly for precise opticalcharacterization of targets within a process chamber, in accordance withsome implementations of the present disclosure.

FIG. 9 depicts a block diagram of an example processing system capableof supporting real-time detection of particulate contaminants presentinside a deposition chamber, based on light scattering data.

DETAILED DESCRIPTION

The implementations disclosed herein provide for accurate broadbandoptical endpoint control of semiconductor device manufacturing. Theimplementations provide for a delivery, into a process chamber, of abeam of light that has a uniform spatial profile for a broad range ofwavelengths. For example, the width of the beam may be the same for a250 nm spectral component of the beam as for a 750 nm spectral componentof the beam. The spatial uniformity of the beam can be achieved bydelivering a light signal through a collimator equipped with a broadbandachromatic lens. This enhanced uniformity ensures a more accuratemeasurement (compared with a collimator deploying conventional opticalelements) of the optical response of a target (such as a substrate)inside the process chamber, and, therefore, a more accuratedetermination of the state of the target (e.g., during substrate etchingor deposition processing).

The collimator may be further equipped with a precision adjustmentmechanism to adjust an alignment of the optical axis of the collimator,for maximizing the efficiency of the incident light delivery to anintended region on the target located within the process chamber. Insome implementations, after maintenance of the process chamber isperformed, the adjustment mechanism may be used to compensate for smalldifferences in positions of the processing tools (such as a variation inpositioning of a chuck for wafer support) caused by disassembly,reassembly, and/or recalibration of the tools.

During electronics device manufacturing, a number of pattern transferoperations, including lithography and etching, are often performed. Forexample, in the lithographic step, a photoresist layer partiallyprotected with a photomask (containing the desired pattern) may beexposed to a light source and subsequently developed in a suitablechemical solution to remove exposed unprotected portions of thephotoresist. The resulting patterned photoresist layer may then be used,in the etching step, as a mask to protect a substrate (such as a siliconwafer) exposed to a reactive (e.g. wet or dry etching) environment toremove the unprotected portions of the substrate. During etching,endpoint data from the substrate (such as optical response data, whichmay include reflectance data, polarization data, and so on) may be usedto determine whether the process is operating according tospecifications, and whether the desired results such as etch depth anduniformity are achieved.

Changes in the reactive environment (such as composition, temperature,density of plasma) and differences in photomask patterns may result invariations in the speed and uniformity of etching. Tracking andresponding to such changes may involve precise and adjustable opticalendpoint systems capable of collecting accurate and substantial opticalresponse data characterizing various target surfaces (wafers,photomasks, and the like) within the process chambers. The goal ofaccuracy is further driven by ever-decreasing dimensions ofmicroelectronic devices, increasingly complex designs of photomasks, andthe raising demands for device uniformity. The existing optical systemsfor endpoint control are often incapable of meeting such increasedtechnological demands.

Aspects and implementations of the present disclosure address this andother shortcomings of the optical inspection technology that may be usedin substrate manufacturing. Described herein is a spatially adjustableoptical inspection device capable of delivering a beam of light with auniform spatial profile within a broad range of wavelengths, for preciseoptical characterization of substrate processing. The implementationsdisclosed herein help to accurately determine optical, physical, and/ormorphological properties of the substrates, such as the substrates’uniformity, smoothness, thickness, refractive index, reflectivity, andso on, and provide an efficient quality control tool that does not callfor slowing down the manufacturing process.

The disclosed implementations pertain to a variety of manufacturingtechniques that use process chambers (that may include depositionchambers, etching chambers, and the like), such as chemical vapordeposition techniques (CVD), physical vapor deposition (PVD),plasma-enhanced CVD, plasma-enhanced PVD, sputter deposition, atomiclayer CVD, combustion CVD, catalytic CVD, evaporation deposition,molecular-beam epitaxy techniques, and so on. The disclosedimplementations may be employed in techniques that use vacuum depositionchambers (e.g., ultrahigh vacuum CVD or PVD, low-pressure CVD, etc.) aswell as in atmospheric pressure deposition chambers.

FIG. 1 illustrates schematically a manufacturing machine 100 thatincludes a spatially adjustable broadband collimator assembly, forprecise optical characterization of targets within a process chamber, inaccordance with some implementations of the present disclosure. In oneimplementation, the manufacturing machine 100 includes a process chamber102 inside a process chamber housing 104 for processing (e.g.,deposition, lithography, etching, and the like) of one or moresubstrates 106. During processing, the substrate 106 may be exposed to aplasma environment 110 for plasma-enhanced processing, e.g., etching.The substrate 106 may be supported by a chuck 108. The process chamber102 may include one or more process kit tools 112, such as an edge ringor the like. The substrate 106 may be lifted by lift pins (not shown) toachieve a target exposure of the back surface of the substrate 106 tothe processing environment, to heat the substrate 106 (e.g., bydirecting light thereon), and so on.

The processing of the substrate 106 in the process chamber 102 can beoptically monitored by an endpoint optical system that includes acollimator assembly 120 and a control module 130. The collimatorassembly 120 may be mechanically coupled to the process chamber housing104 (rigidly or operatively, as explained in more detail below) and maybe optically interfaced with the environment of the process chamber 102,such as the plasma environment 110. The optical interface between thecollimator assembly 120 and the process chamber 102 may be an orifice, aconverging or diverging lens, a transparent slab (which may have nooptical power), a polarizer, or any other device or material that iscapable of transferring light between the collimator assembly 120 andthe process chamber 102. Herein, “light” refers to electromagneticradiation of any spectral range, including visible, far and nearinfrared (IR), far and near ultraviolet (UV), etc. “Light” may furtherinclude unpolarized (e.g., natural) light, linearly, circularly, orelliptically polarized light, partially-polarized light, focused light,diverging light, collimated light, and so on.

The light beam 122 can be produced by the collimator assembly 120 fromin input light 124 generated by a light source 132. In someimplementations, the input light 124 is delivered via one or more inputoptical fiber(s). The light source 132 may be a narrow-band lightsource, such as a light-emitting diode, a laser, a light bulb, etc. Insome implementations, the light source 132 is a broadband light source.In some implementations, the light source 132 includes more than onecomponent light sources, such as multiple narrow-band light sourcesproducing (when taken together) a broadband input light 124. The lightsource 132 may include additional optical elements to control a spectraldistribution and/or polarization of the input light 124 (such asfilters, absorbers, polarizers, etc.).

In some implementations, the input light 124 is converted by thecollimator assembly 120 into the light beam 122, e.g., by making theinput light 124 pass via a plurality of optical elements of thecollimator assembly 120, such as lenses, reflectors, filters, apertures,and so on. The collimator assembly 120 may have broadband properties.More specifically, the collimator assembly 120 may produce (as describedin more detail below) the light beam 122 whose spatial extent may be thesame for multiple spectral component of the beam. For example, adiameter of the produced light beam 122 may be the same within a broadrange of wavelengths λ of various spectral components contained in theinput light 124 and, therefore, in the light beam 122. In existingendpoint detection systems, the diameter of the conventional light beam122-1 varies depending on the wavelength λ. For example, a greencomponent (λ=550 nm) may have a diameter of 9 mm whereas a red component(λ=650 nm) may have a diameter of 13 mm. (This is illustratedschematically in FIG. 1 with the varying shading in the depiction of theconventional light beam 122-1.) As a result, different spectralcomponents propagate along different optical paths. This can result in asignificant error in the obtained reflectivity R(λ) of the substrate,which may, therefore, lead to mischaracterization of the target (e.g.,the surface of the substrate 106) and to errors in the etching process(such as causing the etching to be stopped too early or too late).

In contrast, the implementations of the present disclosure describebroadband collimator assembly 120 that ensures a substantially the samespatial extent of various spectral components λ of the light beam 122.This is illustrated schematically in FIG. 1 with the uniformly whitecross section of the achromatic beam 122-2. To achieve an output of suchbroadband achromatic light beam, the collimator assembly 120 may haveone or more achromatic lenses, as described in more detail below, inreference to FIG. 2 . More specifically, the achromatic beam 122-2 maybe characterized by specifying the beam’s spectral content for multiplespectral ranges Δλ, such as spectral ranges of width Δλ =100 nm (or 150nm, 200 nm or any other range of wavelengths). The spectral ranges maybe centered at a sequence of central wavelengths λ₁, λ₂, λ₃, ... In someimplementations, the ranges are overlapping with Δλ being greater thanthe distance between the adjacent central wavelengths. In someimplementations, Δλ is equal to the distance between the centralwavelengths (e.g., Δλ= λ₃ - λ₂). In some implementations, Δλ is greaterthan the distance between the central wavelengths (so the ranges arenon-overlapping). In some implementations, the ranges Δλ has unequalwidth. (Alternatively, the ranges may correspond to equal frequencyintervals, Δf.) In some implementations, the ranges Δλ correspond toactual emission ranges of various light emitters of the light source 132(e.g., emission ranges of light-emitting diodes of the light source132). In other implementations, the ranges Δλ are defined forcharacterization purposes only and may not be restricted to any specificphysical light emitters.

The spectral components within the range Δλ_(k) centered around λ_(k)may propagate in the form of a spectral beam of some diameter d_(k).(For the sake of conciseness, the beams will be described as havingcircular cross sections. However, it shall be understood that similarcharacterization can be made for beam of any other cross sections, suchas elliptic beams or beams having some other shape.) The k-th spectralbeam may illuminate a k-th region A_(k) on the target surface (e.g.,surface of the substrate 106). The notation A_(k) may stand for the areaof the illuminated region or to some other geometric characteristic ofthe illuminated region. The diameter and/or the area of the k-thilluminated region may be defined using any suitable scheme, as long asthe same scheme is used across various spectral ranges. For example, ahalf-width or a full width of a continuous distribution of the k-thspectral beam intensity may be used to determine the diameter d_(k). Insome implementations, to be substantially the same, two illuminatedregions A_(k) and A_(m) are to have an overlap of at least 90% (or 85%,95%). That is, the part of the region A_(k) that falls outside theregion A_(m) (and vice versa is to be less that 10% (or 15%, 5%) of theregion A_(k).

In some implementations, to possess achromatic broadband properties, thecollimator assembly 120 is to produce at least two spectral beams thatilluminate substantially the same regions on the target surface. In someimplementations, for the collimator assembly 120 to have achromaticbroadband properties, the two spectral beams correspond to the rangesthat are separated by at least 200 nm center-to-center wavelengthseparation. In some implementations, to possess achromatic broadbandproperties the collimator assembly 120 is to produce at least threespectral beams that illuminate substantially the same regions on thetarget surface. In some implementations, the three spectral beamscorrespond to the ranges that are separated by at least 400 nmwavelength separation between the centers of the two outermost ranges.

The light reflected off the target surface may pass through thecollimator assembly 120 in the reverse direction and be collected by oneor more second optical fiber(s). The second optical fiber may deliverthis output light 126 to a light detector 134 for spectral analysis. Thelight detector 134 may include one or more spectrographs, spectrometers,diffraction gratings, mirrors, lenses, photodiodes, and other devices.The light detector 134, alone or in conjunction with a processing device136 (e.g., a central processing unit (CPU), a microcontroller, anapplication-specific integrated circuit (ASIC), a digital signalprocessor (DSP, a field-programmable gate array (FPGA), or any othertype of a processing device), may determine one or more opticalresponses of the target. The optical responses may include thereflectivity R(λ), the refraction index n(λ), or any other opticalquantity that may be used to characterize the substrate, such as apolarization dependence of the reflectivity, an angle of rotation of thepolarization plane upon reflection, luminescence intensity, and so on.

The processing device 136 may be in communication with a memory device138. In some implementations, the memory device 138 stores instructionsthat the processing device 136 is to execute to cause the light source132 to produce the input light 124, to cause the light detector 134 toperform detection of the output light 126, and to perform any furtheroperations that may be needed for substrate processing. Such operationmay include starting, stopping, and/or resuming etching, lithography, ordeposition operations. The processing device 136 may be the sameprocessing device that controls the operations in the process chamber102 or a separate dedicated processing device of the endpoint detectionsystem.

In some implementations, the collimator assembly 120 is equipped with atilt adjustment mechanism 128 to allow adjustment of the optical axis(depicted with a dashed line in FIG. 1 ) of the collimator to facilitatecentering (or re-centering) of the collimator after maintenance or toensure chamber-to-chamber consistency, when the collimator assembly 120is being moved to different process chamber. In some implementations, asdescribed below in reference to FIGS. 4-6 , the tilt adjustmentmechanism 128 includes one or more adjustment screws that facilitate aconfigurable connection between the collimator assembly 120 and theprocess chamber housing 104.

FIG. 2 illustrates schematically an exemplary achromatic (broadband)collimator assembly 200, for precise optical characterization of targetswithin a process chamber, in accordance with some implementations of thepresent disclosure. FIG. 2 is not drawn to scale and is intended as aschematic depiction only. Some elements shown in FIG. 2 may be omittedin various implementations. Some additional elements, known to a personskilled in the optical detection technology may not be shown in FIG. 2for clarity and conciseness, but may actually be present in variousimplementations. In some implementations, the collimator assembly 200corresponds to the collimator assembly 120 of FIG. 1 . The collimatorassembly 200 may have a collimator housing 202. The collimator housing202 may have a chamber interface 204 for coupling of the collimatorassembly 200 to a process chamber (such as the process chamber 102). Thechamber interface 204 may be permanently fused with the collimatorhousing 202 or may be an extension of the collimator housing 202, insome implementations. In some implementations, the chamber interface 204is removably attached to the collimator housing 202 by a thread, or heldto the collimator housing by friction, or retention screws, pins,detents, and the like. The chamber interface 204 may fit to a receivingorifice in the process chamber housing 102 and may be sealed (by one ormore gas-proof seals or gaskets) to the receiving orifice to preventescape of gases from the environment of the process chamber. In someimplementations, the chamber interface 204 is sealed to the orifice inthe process chamber housing 102 with the seal(s) allowing the axis ofthe collimator housing 202 to be tilted away from the vertical directionwithin set limits, but without breaking the isolation of the environmentinside the process chamber 102 from the outside atmosphere.

The collimator housing 202 may define an enclosure to host variousoptical elements of the collimator assembly 200, such as an achromatic(broadband) lens 210, an optical filler 212, an optical interface 214,and so on. As depicted, the top of the collimator housing 202 may havean opening to guide one or more optical fibers 208 (to deliver the inputlight 124 and/or to receive the output light 126) via a conduit in theguiding cap. In some implementations, the optical fiber(s) 208 mayaccess the enclosure of the collimator assembly differently, e.g.,through a sidewall of the housing 202. The optical interface 214 mayinclude an opening, a waveguide, a lens, and so on. The opticalinterface 214 may be configured to allow passage of light but preventaccess of contaminants. For example, upon exiting the optical fiber 208,the input light 124 may pass through a slab (film) of an opticallytransparent material or a diverging (converging) lens, whichmechanically seals the conduit of the optical fiber.

The achromatic lens 210 may be a broadband lens designed to minimizechromatic aberration for a wide range of wavelengths. For example, theachromatic lens 210 may have multiple lenses made of differentmaterials, with some of the materials having a higher dispersion of therefractive index and some of the materials having a lower dispersion. Insome implementations, the achromatic lens 210 may be a doublet lenshaving two optical elements (e.g., a converging lens and a diverginglens). In some implementations, as depicted in FIG. 2 , the achromaticlens 210 may be a triplet lens having three optical elements. In someimplementations, the achromatic lens 210 may have more than threeoptical elements. The achromatic lens 210 may be designed for two,three, or more, reference wavelengths Λ₁, Λ₂, A₃... to have the samefocus (some or all of the reference wavelength may be the centralwavelengths used for characterization of the light beam 122, asdescribed in reference to FIG. 1 ). This may ensure that the chromaticaberration remains small even for wavelengths that fall between thereference wavelengths. The focusing distance(s) of various elements ofthe achromatic lens 210 may be so chosen that the input light deliveredvia the optical fiber(s) 208 becomes a collimated beam after passingthrough the achromatic lens 210. In other implementations, the (properlychosen) distance between the optical fiber 208 and the achromatic lens210 may be used to ensure that the output beam (e.g., the beam 122-2) iscollimated. In some implementations, one or more lens of the opticalinterface 214 facilitates collimation.

In some implementations, the achromatic lens 210 is held within thecollimator housing 202 by a retaining ring. In some implementations, theachromatic lens is screwed into a threated part of the collimatorhousing 202. In some implementations, the achromatic lens 210 isfrictionally held by the collimator housing 202. For example, thediameter of the achromatic lens 210 may be precisely tailored to theinner diameter of the enclosure formed by the collimator housing 202 sothat the lens remains under lateral tension sufficient to generateenough friction to hold the lens securely in place. In someimplementations, the space between the achromatic lens 210 and theoptical interface 214 is filled with a transparent optical filler 212 toensure optical path consistency (e.g., to minimize the presence of air,moisture, and other possible contaminants along the optical paths of theinput and output light signals).

FIG. 3 illustrates schematically advantages of using achromatic(broadband) collimators for precise optical characterization of targetswithin a process chamber, in comparison with a conventional collimator,in accordance with some implementations of the present disclosure. Shownin FIG. 3A are depictions of reflectivity R(λ) data for a referencesubstrate obtained for a continuum of wavelengths λ ranging from near-UVto near-IR (such as a range of 200-800 nm, in one example). The measureddata illustrated schematically in FIG. 3A is obtained using aconventional collimator that does not deploy an achromatic lens. Thedashed line indicates a reference reflectance of the same referencesubstrate obtained by high-precision reflectance measurements in alaboratory setting using high-grade light sources and light detectionspectrometers. The solid line in FIG. 3A illustrates data obtained usinga conventional collimator that produces a beam (such as the beam 122-1)whose spatial extent is not controlled for different wavelengths. As thecomparison of the two curves indicates, while the measured reflectanceis reasonably close to the exact reference reflectance in the UV rangeand the blue part of the visible range, the accuracy deterioratessignificantly in the red part of the visible spectrum and becomes poorin the IR range.

Shown in FIG. 3B are results of measurement of the reflectance R(λ) forthe same reference substrate using a broadband collimator with anachromatic lens, as described above in reference to FIGS. 1-2 . Theimprovement illustrated in FIG. 3B arises from illuminating the targetsubstrate with a beam (such as the beam 122-2) having substantially thesame spatial extent for the entire continuum of wavelengths λ used inthe target characterization. The following table illustrates theimprovement in the beam uniformity for several wavelengths.

Collimator type Beam diameter (in arbitrary units d) 250 nm (near-UV)550 nm (green) 750 nm (near IR) Conventional 0.5d d 1.5d Broadband d d d

The improved beam uniformity contributes to a better accuracy indetermination of the reflectivity R(λ). Because of the more accuratemeasurements of the reflectivity, the processing device 136 may becapable of a precise determination of the current state of the processoperation (deposition, etching, and the like) performed on actualsubstrates in the process chamber 102.

Shown in FIG. 3C is a depiction of a spatial extent of a conventionalbeam (such as the beam 122-1) having two exemplary spectral components,indicated as visible light (e.g., 550 nm) and near-IR light (e.g., 750nm). The position indicated by the horizontal axis may be a radialdistance from the center of the beam. As depicted, the spatial extent(e.g., the distance corresponding to a half-width of the beam) of thetwo spectral components may differ significantly. In contrast, shown inFIG. 3D is a depiction of a spatial extent of a beam (such as the beam122-2) output by a broadband collimator assembly (e.g., assembly 120),for the same two spectral components. As depicted, the spatial extent ofthe two spectral components is substantially the same.

FIG. 4 illustrates schematically an exemplary collimator assembly 400having adjustable alignment, for precise optical characterization oftargets within a process chamber, in accordance with someimplementations of the present disclosure. FIG. 4 is not drawn to scaleand is intended as a schematic depiction only. Some elements shown inFIG. 4 may be omitted in various implementations. Some additionalelements, known to a person skilled in the optical detection technologymay not be shown in FIG. 4 for clarity and conciseness, but may actuallybe present in various implementations. In some implementations, thecollimator assembly 400 may be the collimator assembly 200 of FIG. 2 .The collimator assembly 400 may be configured to optically couple to aprocess chamber (such as the process chamber 102). The collimatorassembly 400 may include a collimator housing 402. The collimatorhousing 402 may have a chamber interface 404 for coupling to the processchamber. The chamber interface 404 may allow a degree of variability(within set limits) in the direction of the collimator axis (which mayalso be the optical axis of the collimator contained within theenclosure formed by the collimator housing 402).

FIG. 5 illustrates schematically a tilted exemplary collimator assembly500 having adjustable alignment, for precise optical characterization oftargets within a process chamber, in accordance with someimplementations of the present disclosure. As shown in FIG. 5 , thecollimator axis 405 may be tilted to angle θ from a reference axis 407(shown by the dashed line). Depicted in FIG. 5 is the vertical referenceaxis 407, but in various implementations, the orientation of thereference axis may have any other suitable direction. For example, insome implementations, where the collimator assembly 400 is coupled to asidewall of the process chamber 102, the reference axis may behorizontal. The tilt angle shown in FIG. 5 is exaggerated for the easeof illustration. In some implementations, the maximum tilt angle may be1° (or some a fraction of 1°). In some implementations, the tilt anglemay be greater than 1° and may be limited by a number of factors, suchas an anticipated need for large tilt angles and the ability of a givenchamber interface 404 to maintain proper gas seal with the processchamber 102.

In some implementations, the tilt adjustment mechanism include one ormore adjustment mechanism 403 to control tilt (alignment) of thecollimator axis 405. “Adjustment mechanism” herein means any mechanicaldevice (such as a screw, a bolt, a lever, a wedge, and the like), or acombination of mechanical devices, that is capable of convertingrotational motion of a control head (e.g., the head of a screw, a knob,etc.) into a parallel motion of a mechanical member (such as a shaft ofthe screw, a spring, a wedge, etc.). The mechanical member may interfacebetween a movable part of the collimator housing 402 and a stationarypart of the collimator housing. In some implementations, the mechanicalmember interfaces directly between the movable part of the collimatorhousing 402 and the process chamber housing 104 (or any part attachedthereto). In some implementations, for precise control of the collimatortilt angle θ, the adjustment mechanism 403 may be outfitted withmicrometer heads or any other devices that provide a suitable feedbackabout the tilt angle and allow reproducible adjustment of the collimatorassembly 400. Because, geometrically, any three arbitrarily placedpoints define a plane, the number of adjustment mechanism 403 is three,in some implementations. In some implementations, the number ofadjustments mechanism 403 is less than three. For example, theadjustment screw 403(1) may be replaced with a non-adjustable screw (ora pin) that maintains a fixed contact with the process chamber housing,whereas the adjustment mechanism 403(2) and 403(3) (not shown in FIGS.4-5 ) may nonetheless allow a fully adjustable tilt control. As aresult, the collimator axis 405 may still be tilted in two directions,allowing both the tilt θ of the collimator axis away from the referenceaxis 407 as well as an azimuthal rotation ϕ around the reference axis.

FIG. 6 illustrates schematically a side view 600 of an exemplarycollimator assembly having adjustable alignment, in accordance with someimplementations of the present disclosure. FIG. 6 is not drawn to scaleand is intended as a schematic depiction only. Some elements shown inFIG. 6 may be omitted in various implementations. Some additionalelements, known to a person skilled in the optical detection technologymay not be shown in FIG. 6 for clarity and conciseness, but may actuallybe present in various implementations. In some implementations, the sideview 600 may be of the collimator assembly whose top view 500 is shownin FIG. 5 .

As depicted in FIG. 6 , in some implementations, the first housingsupport 602-1 may be rigidly coupled to the collimator housing 602. Thesecond housing support 602-2 may be attached to the process chamberhousing (not shown). One or more of the tilt adjustment screws 603 maybe operably coupling the first housing support 602-1 to the secondhousing support 602-2. In some implementations, tension springs 614 areused in conjunction with the adjustment screws 603, in illustrated. Insome implementations, the tension springs 614 are positioned atdifferent locations than the locations of the adjustment screws 606. Thetension springs 614 may remain in the compressed states so that thetotal force exerted (upwards) on the first housing support 602-1 isgreater (in some implementations, significantly greater) than the totalweight of the collimator assembly. Such spring compression may beadvantageous to stabilize the first support relative to the secondsupport and prevent the collimator assembly from wobbling duringoperations of the endpoint detection device. Operations of one or moreof the alignment screws 603 may result in a desired tilt of the opticalaxis of the collimator, similar to operations described in relation toFIG. 4 above.

To accommodate a motion of the first housing support 602-1 relative tothe second housing support 602-2, a tilt-enabling gap 616 may beimplemented. The tilt-enabling gap 616 may extend symmetrically around acircumference of the housing 602 (if the housing has a cylindricalshape) or may be designed to be asymmetric. When one or more tiltadjustment screws are operated (e.g., by a human operator) and thehousing 602 is tilted, as a result, the tilt may be freely allowed untilfurther adjustment is arrested by the body of the housing making acontact with the second housing support 602-2. The amount of the gap 616may be set to allow a maximum pre-determined tilt. For example, if theheight of the second housing support 602-2 near the gap 616 is 0.3 in,the gap of 0.005 may allow up to 1° tilts away from the reference (e.g.,vertical) direction (in addition to a full 360° azimuthal tilt).

FIG. 7 is a flow diagram of one possible implementation of a method 700of deploying a broadband collimator assembly for precise opticalcharacterization of targets within a process chamber, in accordance withsome implementations of the present disclosure. In some implementations,the broadband collimator assembly is spatially adjustable. Method 700may be performed using systems and components described in FIGS. 1-6 orany combination thereof. Some or all blocks of method 700 may beperformed responsive to instructions from the processing device 136, insome implementations. The processing device 136 may be coupled to one ormore memory devices 138. In some implementations, method 700 may beperformed when a substrate is being processed in the process chamber102. In some implementations, method 700 may be performed when acalibration device or a reference substrate is in the process chamber102.

Method 700 may involve outputting, by a source of light, a light signal(operation 710). In some implementations, the processing device (e.g.,device 136) causes the source of light to output the light signal. Inother implementations, a human operator causes the light signal to beoutput. The light signal may have a broad spectral distribution (or be acollection of multiple narrow-band distributions). The light signal mayinclude a number of ranges of wavelengths, such as [λ_(j) - Δλ_(j)/2,λ_(j) + Δλ_(j)/2] where j=1, 2, 3... Each range may be characterized byits central wavelength λ_(j) and width Δλ_(j). Each range may contain aplurality of spectral components. The number of components within eachrange may be very large or even infinite as the spectral components maybe represent a continuum (which may be characterized by a Fourierintegral).

At operation 720, method 700 may continue with directing the firstplurality of spectral components of light belonging to the interval[λ₁ - Δλ₁/2, λ₁ + Δλ₁/2] onto a target surface to cause a first regionon the target surface to be illuminated. Similarly, at operation 730,method 700 may continue with directing the second plurality of spectralcomponents of light belonging to the interval [λ₂ - Δλ₂/2, λ₂ + Δλ₂/2]onto the target surface to cause a first region on the target surface tobe illuminated. The first plurality of spectral components and thesecond plurality of spectral components may be delivered, via (one ormore) first optical fiber(s), to a broadband collimator. The collimatormay have an achromatic lens. After passing through the broadbandcollimator, the first beam (which can be a collimated beam, a focusedbeam, or a diverging beam) that includes the first plurality of spectralcomponents may have a substantially the same cross section as the secondbeam that includes the second plurality of spectral components. As aresult, a first region on the target surface (e.g., a substrate beingetched or otherwise processed) illuminated by the first beam may besubstantially the same as a second region on the target surfaceilluminated by the second beam. Operations 720 and 730 may be performedin an arbitrary order. In some implementations, operations 720 and 730may be performed concurrently. In some implementations, operations 720and 730 may be performed sequentially, one after another.

Each beam directed at the target surface may cause a respectivereflected beam to propagate back through the collimator and be receivedby (one or more) second optical fiber(s), to be transferred to a lightdetector. More specifically, at operation 740, the first reflected beam(that includes a first plurality of reflected, from the target surface,spectral components of light) may be collected, by the second opticalfiber(s). Similarly, at operation 750, the second reflected beam (thatincludes a second plurality of reflected, from the target surface,spectral components of light) may be collected, by the second opticalfiber(s). The first (second) reflected beam may be produced by the first(second) plurality of spectral components of light incident on thetarget surface. Operations 740 and 750 may be performed in an arbitraryorder. In some implementations, operations 740 and 750 may be performedconcurrently. In some implementations, operations 740 and 750 may beperformed sequentially, one after another.

At operation 760, method 700 may continue with receiving, by a lightdetector, via the second optical fiber, the first plurality of reflectedspectral components of light and the second plurality of reflectedspectral components of light. At operation 770, the light detector (inconjunction with the processing device and/memory, in someimplementations) may determine a reflectance of the target surface,based on the received first plurality of reflected spectral componentsof light and the received second plurality of reflected spectralcomponents of light. The reflectance may be determined for the entirewidth of the first range of wavelengths and the entire second range ofwavelengths, in some implementations. In some implementations,additional (e.g., third, fourth, etc.) ranges of wavelengths mayadditionally be used in a way that is similar to the above-describedmethod, to obtain a more accurate characterization of the targetsurface. In some implementations, the first range is within a 400-700 nminterval of wavelengths and the second range is outside the 400-700 nminterval of wavelength. In some implementations, the third range isoutside the 400-700 nm interval of wavelength and is different from thesecond range. In some implementations, the second (or third) range iswithin a 100-400 nm interval and the third (second) range is within a700-900 nm of wavelengths.

FIG. 8 is a flow diagram of one possible implementation of a method 800of adjusting tilt of an adjustable collimator assembly for preciseoptical characterization of targets within a process chamber, inaccordance with some implementations of the present disclosure. In someimplementations, method 800 is performed using systems and componentsdescribed in FIGS. 1-6 or any combination thereof. Some or all blocks ofmethod 800 may be performed responsive to instructions from theprocessing device 136, in some implementations.

At operation 810, method 800 may detect a process chamber setup event.For example, the process chamber may have been serviced (e.g., ascheduled or an unscheduled maintenance may have been performed), one ormore components of the process chamber may have been replaced, or acollimator assembly may have been moved and coupled to a differentchamber. In some implementations, “setup event” may be a setup checkevent that is not associated with any setup modifications, but may be anindication of a scheduled routine check-up (or a check-up requested by ahuman operator).

At operation 820, method 800 may continue with outputting an incidentbeam of light at a target via the (adjustable) collimator assembly. Forexample, one or more sources of light may produce light beams. The lightbeams may be delivered (e.g., via one or more input optical fibers) tothe collimator assembly and, having, passed through optical componentsof the collimator assembly, may be directed onto the target. The targetmay be a calibration device, a reference substrate with known opticalproperties, or a regular substrate that is about to undergo processing(e.g., etching), provided that the optical properties of such asubstrate are known.

The incident beams may cause a reflected beam to be generated by thetarget. The reflected beam may pass (in reverse direction) through theoptical components of the collimator and may be delivered, via one ormore output optical fibers, to a light detector. At operation 830, thelight detector may determine intensity of the reflected beam. Atoperation 840, a processing device in communication with the lightdetector and a memory device, may retrieve, from the memory device,calibration data for the target. In some implementations, thecalibration data may include the reflectivity of the target as afunction of the angle of incidence of the incident beam. At operation850, method 800 may continue with the processing device performing acomparison of the intensity data, obtained from the light detector, withthe calibration data, retrieved from the memory device. As a result, theprocessing device may determine a degree of misalignment of thecollimator assembly (e.g., because of the performed process chambersetup modification). For example, the reflectivity may decrease (orincrease) with the degree of misalignment.

At operation 860, method 800 may output a tilt adjustment value to beapplied to the tilt adjustment mechanism of the collimator assembly tocorrect the determined misalignment of the collimator assembly. Theoutput value may be accessed by a human operator who may correct thealignment of the collimator assembly in view of the output value.

FIG. 9 depicts a block diagram of an example processing device 900operating in accordance with one or more aspects of the presentdisclosure. The processing device 900 may be the processing device 136of FIG. 1 , in one implementation. Example processing device 900 may beconnected to other processing devices in a LAN, an intranet, anextranet, and/or the Internet. The processing device 900 may be apersonal computer (PC), a set-top box (STB), a server, a network router,switch or bridge, or any device capable of executing a set ofinstructions (sequential or otherwise) that specify actions to be takenby that device. Further, while only a single example processing deviceis illustrated, the term “processing device” shall also be taken toinclude any collection of processing devices (e.g., computers) thatindividually or jointly execute a set (or multiple sets) of instructionsto perform any one or more of the methods discussed herein.

Example processing device 900 may include a processor 902 (e.g., a CPU),a main memory 904 (e.g., read-only memory (ROM), flash memory, dynamicrandom access memory (DRAM) such as synchronous DRAM (SDRAM), etc.), astatic memory 906 (e.g., flash memory, static random access memory(SRAM), etc.), and a secondary memory (e.g., a data storage device 918),which may communicate with each other via a bus 930.

Processor 902 represents one or more general-purpose processing devicessuch as a microprocessor, central processing unit, or the like. Moreparticularly, processor 902 may be a complex instruction set computing(CISC) microprocessor, reduced instruction set computing (RISC)microprocessor, very long instruction word (VLIW) microprocessor,processor implementing other instruction sets, or processorsimplementing a combination of instruction sets. Processor 902 may alsobe one or more special-purpose processing devices such as an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), a digital signal processor (DSP), network processor, or thelike. In accordance with one or more aspects of the present disclosure,processor 902 may be configured to execute instructions implementingmethod 700 of deploying a broadband collimator assembly, for preciseoptical characterization of targets within a process chamber and/ormethod 800 of adjusting tilt of an adjustable collimator assembly.

Example processing device 900 may further comprise a network interfacedevice 908, which may be communicatively coupled to a network 920.Example processing device 900 may further comprise a video display 910(e.g., a liquid crystal display (LCD), a touch screen, or a cathode raytube (CRT)), an alphanumeric input device 912 (e.g., a keyboard), aninput control device 914 (e.g., a cursor control device, a touch-screencontrol device, a mouse), and a signal generation device 916 (e.g., anacoustic speaker).

Data storage device 918 may include a computer-readable storage medium(or, more specifically, a non-transitory computer-readable storagemedium) 928 on which is stored one or more sets of executableinstructions 922. In accordance with one or more aspects of the presentdisclosure, executable instructions 922 may comprise executableinstructions implementing method 700 of deploying a broadband collimatorassembly, for precise optical characterization of targets within aprocess chamber and/or method 800 of adjusting tilt of an adjustablecollimator assembly.

Executable instructions 922 may also reside, completely or at leastpartially, within main memory 904 and/or within processor 902 duringexecution thereof by example processing device 900, main memory 904 andprocessor 902 also constituting computer-readable storage media.Executable instructions 922 may further be transmitted or received overa network via network interface device 908.

While the computer-readable storage medium 928 is shown in FIG. 9 as asingle medium, the term “computer-readable storage medium” should betaken to include a single medium or multiple media (e.g., a centralizedor distributed database, and/or associated caches and servers) thatstore the one or more sets of operating instructions. The term“computer-readable storage medium” shall also be taken to include anymedium that is capable of storing or encoding a set of instructions forexecution by the machine that cause the machine to perform any one ormore of the methods described herein. The term “computer-readablestorage medium” shall accordingly be taken to include, but not belimited to, solid-state memories, and optical and magnetic media.

It should be understood that the above description is intended to beillustrative, and not restrictive. Many other implementation exampleswill be apparent to those of skill in the art upon reading andunderstanding the above description. Although the present disclosuredescribes specific examples, it will be recognized that the systems andmethods of the present disclosure are not limited to the examplesdescribed herein, but may be practiced with modifications within thescope of the appended claims. Accordingly, the specification anddrawings are to be regarded in an illustrative sense rather than arestrictive sense. The scope of the present disclosure should,therefore, be determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled.

The implementations of methods, hardware, software, firmware or code setforth above may be implemented via instructions or code stored on amachine-accessible, machine readable, computer accessible, or computerreadable medium which are executable by a processing element. “Memory”includes any mechanism that provides (i.e., stores and/or transmits)information in a form readable by a machine, such as a computer orelectronic system. For example, “memory” includes random-access memory(RAM), such as static RAM (SRAM) or dynamic RAM (DRAM); ROM; magnetic oroptical storage medium; flash memory devices; electrical storagedevices; optical storage devices; acoustical storage devices, and anytype of tangible machine-readable medium suitable for storing ortransmitting electronic instructions or information in a form readableby a machine (e.g., a computer).

Reference throughout this specification to “one implementation” or “animplementation” means that a particular feature, structure, orcharacteristic described in connection with the implementation isincluded in at least one implementation of the disclosure. Thus, theappearances of the phrases “in one implementation” or “in animplementation” in various places throughout this specification are notnecessarily all referring to the same implementation. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more implementations.

In the foregoing specification, a detailed description has been givenwith reference to specific exemplary implementations. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the disclosure asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense. Furthermore, the foregoing use of implementation,implementation, and/or other exemplarily language does not necessarilyrefer to the same implementation or the same example, but may refer todifferent and distinct implementations, as well as potentially the sameimplementation.

The words “example” or “exemplary” are used herein to mean serving as anexample, instance, or illustration. Any aspect or design describedherein as “example” or “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects or designs. Rather, use ofthe words “example” or “exemplary” is intended to present concepts in aconcrete fashion. As used in this application, the term “or” is intendedto mean an inclusive “or” rather than an exclusive “or.” That is, unlessspecified otherwise, or clear from context, “X includes A or B” isintended to mean any of the natural inclusive permutations. That is, ifX includes A; X includes B; or X includes both A and B, then “X includesA or B” is satisfied under any of the foregoing instances. In addition,the articles “a” and “an” as used in this application and the appendedclaims should generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Moreover, use of the term “an implementation” or “oneimplementation” or “an implementation” or “one implementation”throughout is not intended to mean the same implementation orimplementation unless described as such. Also, the terms “first,”“second,” “third,” “fourth,” etc. as used herein are meant as labels todistinguish among different elements and may not necessarily have anordinal meaning according to their numerical designation.

What is claimed is:
 1. A collimator assembly comprising: a collimatorhousing comprising: an interface configured to couple to a processchamber; and a port to receive a first optical fiber, wherein the firstoptical fiber is to deliver, to an enclosure formed by the collimatorhousing, a plurality of spectral components of light; and an achromaticlens located, at least partially, within the enclosure formed by thecollimator housing, the achromatic lens to: direct the plurality ofspectral components of light onto a target surface disposed within theprocess chamber.
 2. The collimator assembly of claim 1, wherein theplurality of spectral components of light comprises: a first set ofspectral components within a 400-700 nm interval of wavelengths, whereinthe first set of spectral components is to illuminate a first region ofthe target surface, and a second set of spectral components outside the400-700 nm interval of wavelengths, wherein the first set of spectralcomponents is to illuminate a second region of the target surface,wherein an overlap between the first region and the second region isleast 90% of each of the first region and the second region.
 3. Thecollimator assembly of claim 2, wherein the plurality of spectralcomponents of light is at least 300 nm wide.
 4. The collimator assemblyof claim 1, wherein the port of the collimator housing is further toreceive a second optical fiber, wherein the second optical fiber is to:collect a plurality of reflected, from the target surface, spectralcomponents of light produced by the plurality of spectral components oflight directed onto the target surface; and deliver the plurality ofreflected spectral components of light to a light detector.
 5. Thecollimator assembly of claim 4, further comprising a conduit to provideaccess of the first optical fiber and the second optical fiber to theenclosure formed by the collimator housing.
 6. The collimator assemblyof claim 1, wherein the achromatic lens is frictionally held within theenclosure formed by the collimator housing.
 7. The collimator assemblyof claim 1, wherein the achromatic lens is a triplet lens.
 8. Thecollimator assembly of claim 1, wherein the plurality of spectralcomponents of light directed onto the target surface by the achromaticlens forms a collimated beam.
 9. The collimator assembly of claim 1,further comprising an optically transparent filler that fills at least apart of the enclosure formed by the collimator housing.
 10. Thecollimator assembly of claim 1, wherein the collimator housing furthercomprises a tilt adjustment mechanism to modify alignment of an axis ofthe collimator housing relative to the process chamber.
 11. Thecollimator assembly of claim 10, wherein the tilt adjustment mechanismcomprises a plurality of adjustment screws, wherein adjustment of eachof the plurality of adjustment screws modifies alignment of the axis ofthe collimator housing.
 12. The collimator assembly of claim 10, furthercomprising a first support rigidly coupled to the collimator housing, asecond support rigidly coupled to the process chamber, and a gap betweenthe first support and the second support, wherein the gap is toaccommodate a motion of the first support caused by modified alignmentof the axis of the collimator housing.
 13. The collimator assembly ofclaim 12, further comprising one or more tension springs to stabilizethe first support relative to the second support.
 14. An endpointdetection system comprising: a source of light to output a plurality ofspectral components of light; a collimator housing comprising: aninterface configured to couple to a process chamber; and a port toreceive a first optical fiber, wherein the first optical fiber is todeliver, to an enclosure formed by the collimator housing, a pluralityof spectral components of light; an achromatic lens located, at leastpartially, within the enclosure formed by the collimator housing, theachromatic lens to: direct the plurality of spectral components of lightonto a target surface disposed within the process chamber; a secondoptical fiber to: collect a plurality of reflected, from the targetsurface, spectral components of light produced by the plurality ofspectral components of light directed onto the target surface; a lightdetector to receive, via the second optical fiber, the plurality ofreflected spectral components of light; and a processing device,communicatively coupled to the light detector, to determine, using thereceived plurality of reflected spectral components of light, one ormore optical characteristics of the target surface.
 15. The endpointdetection system of claim 14, wherein the plurality of spectralcomponents of light comprises: a first set of spectral components withina 400-700 nm interval of wavelengths, wherein the first set of spectralcomponents is to illuminate a first region of the target surface, and asecond set of spectral components outside the 400-700 nm interval ofwavelengths, wherein the first set of spectral components is toilluminate a second region of the target surface, wherein an overlapbetween the first region and the second region is least 90% of each ofthe first region and the second region.
 16. The endpoint detectionsystem of claim 14, wherein the achromatic lens is frictionally heldwithin the enclosure formed by the collimator housing.
 17. The endpointdetection system of claim 14, wherein the achromatic lens is a tripletlens.
 18. The endpoint detection system of claim 14, further comprising:a tilt adjustment mechanism to modify alignment of an axis of thecollimator housing relative to the process chamber.
 19. The endpointdetection system of claim 18, wherein the tilt adjustment mechanismcomprises: a plurality of adjustment screws, wherein adjustment of eachof the plurality of adjustment screws modifies alignment of the axis ofthe collimator housing; and one or more tension springs.
 20. A methodcomprising: delivering, through a port in a collimator housing, aplurality of spectral components of light to an achromatic lens;directing, through the achromatic lens, the plurality of spectralcomponents of light onto a target surface disposed withing a processchamber; collecting, by a second optical fiber, a plurality ofreflected, from the target surface, spectral components of lightproduced by the plurality of spectral components of light directed ontothe target surface; receiving, by a light detector, via the secondoptical fiber, the plurality of reflected spectral components of light;and determining, by a processing device communicatively coupled to thelight detector, using the received plurality of reflected spectralcomponents of light, one or more optical characteristics of the targetsurface.